Several approaches have been utilized to correct for a movement of a subject during scans. Such conventional methods require an off-line, post-processing of the images. Indeed, an image correction is not theoretically possible in some cases because certain areas of k-space may not be sampled, while others are oversampled. The earliest navigator-based methods for the motion correction utilized straight-line navigators to detect a linear motion. Such technique may be useful in chest examinations where the diaphragm and associated organs translate along a particular axis. However, these conventional methods do not quantify and determine the magnitudes or degrees of rotations of the objects being examined, or portions thereof.
Other conventional systems and methods use correlated volumes to calculate rotations and translations. While this technique allows for a correction of certain types of motions, it cannot be applied to three dimensional single image structural scans. Indeed, the techniques employed by these systems and methods are computationally intensive. Similar approaches have been used on-line and off-line for two dimensional sequences. In particular, slices can be correlated to calculate the transformation from one slice to the next, and correct for such changes. However, while this conventional method has certain benefits, the correction of the motion provided therein only applies to the object motion for an in-plane movement.
Another conventional approach for the motion correction utilizes a set of navigator pulses. For example, circular navigators have been proposed to gauge a rotation within sequences. The circular navigators are 30 ms in duration, and three of these circular navigators are required to characterize the motion of the object about three cardinal axes. An iterative approach is then taken to correct the motion of the object since the navigators are not usable for the out of plane rotations. Therefore, this conventional method provides an approximate correction. Another set of three circular navigators is then acquired for a final (fine) adjustment. While this approach fulfills the theoretical need to compensate for all three axes of motions, there are certain impracticalities associated with such conventional approach. Most importantly, the entire procedure is relatively time-consuming, i.e., adding this procedure to, e.g., a standard functional magnetic resonance imaging (“fMRI”) acquisition sequence is not practical.